To test a new method (cross-correlation baroreflex sensitivity, xBRS) for the computation of time-domain baroreflex sensitivity on spontaneous blood pressure and heart interval variability using the EUROBAVAR data set.
We applied xBRS to the 42 records in the EUROBAVAR data set, obtained from 21 patients in the lying and standing positions. One patient had a recent heart transplant and one was diabetic with evident cardiac autonomic neuropathy. xBRS computes the correlation between beat-to-beat systolic blood pressure and R–R interval, resampled at 1 Hz, in a sliding 10 s window, with delays of 0–5 s for interval. The delay with the greatest positive correlation is selected and, when significant at P = 0.01, slope and delay are recorded as one xBRS value. Each 1 s of the recording is the start of a new computation. Non-parametric tests are used.
With patients in the lying position, xBRS yielded a value of 12.4 ms/mmHg compared with the EUROBAVAR sequential 16.2 ms/mmHg, and for the standing positions the respective values were 6.2 and 6.7 ms/mmHg, giving lying to standing ratios of 1.96 and 2.10, respectively. xBRS yielded results for all files, with 20 values per minute on average at a lower within-patient variance. Best delays were 0, 1 and 2 s, and the delay increased by 102 ms when the patient was in the standing position. The xBRS method was successful in the patients with diabetes and the heart transplant.
The xBRS method should be considered for experimental and clinical use, because it yielded values that correlated strongly with and were close to the EUROBAVAR averages, yielded more values per minute, had lower within-patient variance and measured baroreflex delay.
aTNO-TPD-BMI and bDepartment of Physiology, Academic Medical Centre, University of Amsterdam, The Netherlands.
Sponsorship: B.E.W. received a grant towards his PhD thesis from Finapres Medical Systems (FMS), Amsterdam, The Netherlands. J.G. is supported by a grant from Space Research Organisation Netherlands. She received a travel grant from FMS for attending the Monza Conference in 2003. FMS intends to or has built the new algorithm into their commercial Finometer device.
Correspondence and requests for reprints to Berend E. Westerhof, TNO Biomedical Instrumentation, Academic Medical Centre, Suite K2–228, University of Amsterdam, Meibergdreef 9, NL-1105 AZ Amsterdam, The Netherlands. Tel: +31 20 5665838; fax: +31 20 6976424; e-mail: firstname.lastname@example.org
Received 10 July 2003 Revised 2 March 2004 Accepted 25 March 2004
See editorial commentary on page 1259